Always try to use the highest octane available. I prefer to use leaded on my Giuliettas, as it gives extra protection to the valve seats and guides, which don't last very long on these engines.
If your engine is still on the standard compression ratio of 9.0:1 (it will have a deck height of 111,8 mm), you can advance the timing further than the factory recommends. It gives much better driveability. On my blue Giulietta which is 100% standard, we advanced the timing to 14 degrees BTDC, without any pinging and knocking. Throttle response much better at low revs.
Even on my modified Giulietta with a 11:1 compression ratio and Group One cams, I use about 13 degrees BTDC at 1000 rpm. Obviously the secondary advance is much stiffer than standard to prevent knocking.
The nice thing about these engines is that you can play around so much. And it is even better when you can kick the backside of some modern hot hatch!